with regard to those green capacitors it's not just the dielectric insulation resistance that comes into question but also the performance at a given frequency. As flyback tuning capacitors there will be considerable strain on the dielectric, mechanical strain in fact and that's why those capacitors get hot.

405 fan wrote:Hi ChrisThanks I will bring them over some time . I was beginning to think that there was another fault in the set causing this but these green caps are unreliable.Regards.Gary.

It grates on me too when you have a bunch of NOS caps that are not fit for original purpose, but there is the clue, "Not for for original purpose".

In my opinion there is no reason to bin them, they may be perfectly fine for other use in lesser circuit positions and certainly out of the high pulse condition of the line stage. For example I had a number of NOS Philips red cans the 470uF/250VDC ones with the rivet fault that could end up causing the scary EHT blow hole in a CRT. Also I have about 500 NOS .1uF/275VDC RIFA caps and many NOS Plessey blue/whites. Rather than bin all these caps I use them all in low voltage/Low stress application, so far all has been well. Just worth keeping a note in the stock draws to remind others.

I just ordered some 5100PF 2000V Pulse MKP10 Capacitor from CHS as I don't have any in stock and I think my 2100 chassis GEC has the original cap in place. It will be interesting to see if they turn up quicker than your Cricklewoods

Till Eulenspiegel wrote:with regard to those green capacitors it's not just the dielectric insulation resistance that comes into question but also the performance at a given frequency. As flyback tuning capacitors there will be considerable strain on the dielectric, mechanical strain in fact and that's why those capacitors get hot.

Till Eulenspiegel.

This is why polypropylene dielectric caps are used in flyback tuning. Polypropylene has superior performance when dealing with very fast rise/fall times, and also with the inevitable high current that flows - I = C(dv/dt) an' all that. Polyester is only suitable for decoupling or the slow rate of change of audio.

In the 1970s those green Philips flyback capacitors had a dreadful reputation. The original Thorn 8000 series CTV employed one in the line output stage. It wasn't long before a replacement capacitor of a different make was supplied from the TCE service department.It is a very rare event when bad component comes from Philips.

CrustyTV wrote:It grates on me too when you have a bunch of NOS caps that are not fit for original purpose, but there is the clue, "Not for for original purpose".

In my opinion there is no reason to bin them, they may be perfectly fine for other use in lesser circuit positions and certainly out of the high pulse condition of the line stage. ]

I'll second that. I have some of these original Philips caps...all test fine on the bridge with excellent leakage characteristic. Knowing their reputation in pulse circuits, I've used them in other positions with no problems at all. One such has been used as a tone corrector across an output transformer primary for well over 10 years.

Till Eulenspiegel wrote:It is a very rare event when bad component comes from Philips.

Till Eulenspiegel.

True, but remember the yellow tuning caps used in the line output stage of the G11 (9n1 I think)? They used to fail by burning down one side where the lead was welded. Philips components reckoned it was poor welding after investigating and they changed the construction to the later 'box' type capacitor. No problems with those.

Just received and e-mail from CHS, the 5.1nF pulse cap order has been canceled as they are no longer in stock, with no suitable replacement to be found. Gary, I suspect you will encounter the same. Lets hope they amend their website as that was most infuriating

Cathovisor wrote:Gary, have you tried putting some of your NOS ones on a bridge to see what value they come out as?

I found one of those green tuning caps in my stock, out of interest I put it on the bridge at 600V no leakage. Unable to do a value check, the eye is duff so unable to balance. Then onto an insulation test at 1kV it seemed happy, the meter indicating a little over 50MΩ. But as we've discussed earlier hardly indicative of the real harsh working conditions, theses caps would face.

Cathovisor wrote:Given I = C(dv/dt) I wonder just how much current these caps are carrying?

The rise time of the flyback pulse is not a true step function being in the sense of the cosine type of waveform. Nevertheless, there will be a lot of energy in that pulse when one considers first it is stepped up to 8KV to supply the EHT tripler cascade. We know the max beam current is in the order of 1mA @ 25KV. that's 25 watts!Secondly, all that energy contributes to the first 40% of the line scan. That capacitor has a tough job to do.

Hi ChrisI did indeed receive the same email this morning but incredibly the cricklewood ones arrived this morning. I've been at work all day today conduction a couple of friends funerals so I'll try one of these cricklewood caps tomorrow.Regards.Gary.

Hi everyoneI've made a mistake, the caps that came this morning are the ones I ordered from that link that Chris found . The blue ones on ebay, do you think they'll be ok in the GEC ? . The cricklewood caps are still on their way .Regards.Gary

Hi, folks, RR here. I've found some exact replacements for the 5n2, just take a look on vintageparts.com, they've got some, 188 in stock at 95p each. 5%, 1500v. Sorry I don't know how to make a link but they're easy to find, just go on the site and type in 5N2 in the search box. I hope this helps. They've also got some visconol's, .001uF. RR.

On VGA CRTs with there 50Khz line scan circuits even the Phillips blue box pulse caps fail open circuit with a little black sooty spot on the end where the lead is welded on.Those Panasonic dip types fared better though. I have got plenty of Phillips 6n2s left over from my VGA days.

Rebel Rafter wrote:Hi, folks, RR here. I've found some exact replacements for the 5n2, just take a look on vintageparts.com, they've got some, 188 in stock at 95p each. 5%, 1500v. Sorry I don't know how to make a link but they're easy to find, just go on the site and type in 5N2 in the search box. I hope this helps. They've also got some visconol's, .001uF. RR.

I've fitted one of these blue ones today and so far the sets been running for nearly half an hour. The cap is cool, I thought it might have been a little warm. So that's it the restoration is complete. Thanks to everyone for your comments.

Excellent result there Gary, well done.Probably related this but recall when adapting the HMV 2633 16" 960 portable to take a 1400 Lopt when the original red jellypot failed I fitted a NOS 180pF 8Kv disc capacitor to the transformer. 160pF would have been preferred but I didn't have one. The capacitor runs extremely hot. Still works well despite this. Haven't tried another until I can get a suitable 160pF type. These transformers can easily be ruined by heat from the iron as we know.Brian